Tire pyrolysis

Tire recycling, or rubber recycling, is the process of recycling waste tires that are no longer suitable for use on vehicles due to wear or irreparable damage. These tires are a problematic source of waste, due to the large volume produced, the durability of the tires, and the components in the tire that are ecologically problematic. Because they are highly durable and non-biodegradable, they can consume valued space in landfills. In 1990, it was estimated that over 1 billion scrap tires were in stockpiles in the United States. As of 2015, only 67 million tires remain in stockpiles. From 1994 to 2010, the European Union increased the amount of tires recycled from 25% of annual discards to nearly 95%, with roughly half of the end-of-life tires used for energy, mostly in cement manufacturing. Newer technology, such as pyrolysis and devulcanization, has made tires suitable targets for recycling despite their bulk and resilience. End uses for tires include tire-derived fuels, new rubber products, playground surfacing, new tires, and rubber modified asphalt.

The tire life cycle can be identified by the following six steps:

Tires are not desired at landfills, due to their large volumes and 75% void space, which quickly consumes valuable space. Tires can trap methane gases, causing them to become buoyant, or bubble to the surface. This 'bubbling' effect can damage landfill liners that have been installed to help keep landfill contaminants from polluting local surface and ground water.

Shredded tires are now being used in landfills, replacing other construction materials, for a lightweight back-fill in gas venting systems, leachate collection systems, and operational liners. Shredded tire material may also be used to cap, close, or daily cover landfill sites.Scrap tires as a back-fill and cover material are also more cost-effective, since tires can be shredded on-site instead of hauling in other fill materials.

Tire stockpiles create a great health and safety risk. Tire fires can occur easily, burning for months, creating substantial pollution in the air and ground. Recycling helps to reduce the number of tires in storage. An additional health risk, tire piles provide harborage for vermin and a breeding ground for mosquitoes that may carry diseases. Illegal dumping of scrap tires pollutes ravines, woods, deserts, and empty lots; which has led many states to pass scrap tire regulations requiring proper management. Tire amnesty day events, in which community members can deposit a limited number of waste tires free of charge, can be funded by state scrap tire programs, helping decrease illegal dumping and improper storage of scrap tires.

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